The devices to which the invention relates are used in installations for manufacturing containers such as bottles by processes of blowing or stretch-blowing of hot preforms of thermoplastic resin such as PET or PEN, transfer arm (or transfer star) conveying devices being used, in particular, at the entrances of molds for introducing the hot preforms into the molds and at the exits of molds for recovering the containers which have been formed. These operations for introducing the preforms into the molds and recovering formed vessels take place continuously, the two transfer arm devices, at the entry and exit, rotating continuously in synchronization with a rotary carousel supporting the molds, this carousel following the predetermined circular path whose convexity is inverse with respect to the trajectory of the rotary base.
The arrangement of the transfer arms must be such that:                the gripping pincer provided at the end of each arm accompanies the neck of the container (in other words the preform or blank at the entry to the carousel or a container proper, final or intermediate, at the exit from the carousel) over a given angular sector extending on both sides of the point of tangency of the corresponding circular trajectories of the pincer and of the central axis of the molds carried by the carousel, even when these trajectories extend with concavities facing in opposite directions from each other, the sector being required to have a sufficient extension to permit the gripping or release of the container in the mold;        there is no interference between the molds and the containers transported by the arms while the transfer of containers by the arms is taking place.        
The document FR 2 479 077 shows and describes an arrangement of a transfer arm conveyor device (FIGS. 6-12; page 7, line 16 to page 8, line 15, and page 10, line 20, to page 11, line 26). With reference to FIGS. 1 to 3 of the attached drawings (corresponding to FIGS. 8, 10 and 11 of the document FR 2 479 077 respectively), the known conveyor device comprises a rotary plate 1 which carries a plurality of transfer arms 2 distributed regularly over its periphery. These transfer arms 2 are mounted pivotably on the plate 1 by means of corresponding pivot shafts 3. In order to make each transfer arm 2 pivot to both sides of its radial position, each arm 2 is connected solidly to a lever 4 carrying a roller 5 which interacts with, and follows, a fixed cam 6 having a closed curvilinear shape.
Additionally, each transfer arm 2 is made in telescopic form. For this purpose, each arm 2 comprises a stirrup 7 which is connected solidly to the shaft 3 for pivoting on the plate 1. A rod 8 is mounted in a freely slidable way in the stirrup 7, and is returned to a position of minimum elongation by a spring 9 interposed between the said rod 8 and the stirrup 7. The rod 8 is connected solidly to a roller 10 which interacts with, and follows, a fixed cam extending with a closed curvilinear contour, the roller 10 bearing on the cam causing the length of the transfer arm 2 to vary as a function of the contour of the cam during the rotation of the plate 1.
At its free end, the rod 8 supports a pincer 11 for gripping containers, with two pivoting jaws 12, 13, brought towards each other by a spring 14. In the illustrated embodiment, a mechanism for opening the jaws 12, 13 is provided, to act in opposition to the spring 14 in order to enable the containers to be gripped or released easily. This mechanism comprises a link rod 15 pivoted on the pincer 11 and also pivoted on a lever 16 mounted pivotably about a shaft 17 on the stirrup 7. The other end of the lever 16 supports a roller 18 interacting with a fixed cam path defining a curvilinear trajectory 19.
In other known devices, the jaw opening mechanism is not provided, and in this case the gripping or release of the containers by the jaws takes place by force.
In FIG. 3, the trajectory followed by the pivot shaft 3 is indicated by 20.
Because of this structural arrangement and the appropriate shaping of the different cams, the known device can operate in the following manner, which is shown schematically in FIG. 3 of the attached drawings (where the straight line joining the centre of rotation of the device and of the carousel and passing through the point D of tangency of the two circular trajectories is considered to be the reference axis) In FIG. 3, a single transfer arm 2 is shown in a highly schematic way in its different positions during a revolution of the plate 1.
At approximately the beginning of the quarter of the circular trajectory downstream of the point of tangency D (with respect to the direction of rotation of the conveyor device), the transfer arm 2 is made to pivot, being actuated by the roller 5 engaged in the cam 6, so that it advances on its radial position, in other words the free end of the arm 2 supporting the pincer 11 precedes the pivot shaft 3 of the arm 2 on the plate 1. Simultaneously, the rod 8 is actuated by the roller 10, engaged with the corresponding cams, so that it extends with respect to the stirrup 7 in such a way that the transfer arm 2 reaches its maximum length. Thus the pincer 11 is brought, at a point D1 located upstream of the point D, substantially into coincidence with the trajectory of the mold axis upstream of the point of tangency D.
Because of the appropriate shapes of the respective cams guiding the rollers 5 and 10 respectively, the transfer arm 2 is then progressively brought toward its radial position which it reaches when its shaft 3 for pivoting on the plate 1 coincides with the reference axis defined above, at the same time as the rod 8 is progressively retracted into the stirrup 7 and the length of the arm 2 decreases to a minimum when the pivot shaft 3 of the arm reaches a position of coincidence with the reference axis.
Beyond the reference axis, in an inverse movement, the transfer arm 2 is made to pivot upstream (with respect to the direction of rotation), moving progressively away from its radial position, while its length is simultaneously made to increase by the progressive extension of the rod 8 out of the stirrup 7.
Because of this arrangement, the pincer 11 is made to remain in coincidence with the axis of the mold and accompanies the latter through a predetermined angular sector α which is sufficient to enable a preform to be introduced into the mold (at the entrance) or to enable a container to be removed from the mold (at the exit) without interference with the moving parts of the mold and while allowing these moving parts of the mold the time required for their movement (including the closing time for the mold at the entrance and the opening time at the exit).
Variant embodiments of this basic structure have been devised for specific applications; in particular, the document FR 2 802 191 describes a variant with a double gripping pincer for interaction with a double-cavity mold processing two containers simultaneously, in which the double-pincer unit is mounted pivotably at the end of the transfer arm. Other adaptations are indicated in the documents FR 2 709 264, FR 2 731 176 and FR 2 796 588.
It is true that these known arrangements are entirely satisfactory and are currently applied in the aforementioned container manufacturing installations.
However, these arrangements are structurally complex, using, for example, sliding members as part of the structure of the telescopic arms, which generate friction and consequently wear; this results in the progressive development of play which generates vibration and noise. Furthermore, the multiple movements of moving parts require the installation of corresponding cams, which are difficult to manufacture and require an amount of space according to their number.
Above all, the conveyor device designed as described above has a large transverse dimension, and the overall bulk of the conveyor device is even more troublesome because the bulk of the devices located at the entrance of the molding device projects from the unit formed by the installation as a whole.
Finally, the multiplicity of the members and the multiplicity of the movements are such that it is impossible to attempt to make the known conveyor device operate at higher speeds than those currently used, even though there is a strong demand for higher output rates among the users of container manufacturing installations.